排序方式: 共有31条查询结果,搜索用时 15 毫秒
21.
Wheaton CA Eisler DJ Jennings MC Puddephatt RJ 《Journal of the American Chemical Society》2006,128(48):15370-15371
Reactions of the precursor molecules [Au2(mu-BINAP)(O2CCF3)2], 1a, racemic BINAP, 1b, S-BINAP (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) with the easily exchanged linear bis(pyridine) ligand 1,2-trans-bis(4-pyridyl)ethylene (bipyen) gave the polymeric complex [{Au2(mu-R-BINAP)0.5(mu-S-BINAP)0.5(mu-bipyen)}n](CF3CO2)2n, 2a, but either the polymer [{Au2(mu-S-BINAP)(mu-bipyen)}n](CF3CO2)2n, 2b, or the remarkable oligomeric [Au10(mu-S-BINAP)5(mu-bipyen)4(kappa1-bipyen)2](CF3CO2)10, 3, respectively. The type of oligomer 3 is a missing link in the ring-opening polymerization of macrocyclic coordination compounds. 相似文献
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In relativistic nucleus–nucleus collisions the transverse energy per charged particle, ET/Nch, increases rapidly with beam energy and remains approximately constant at about 800 MeV for beam energies from SPS to RHIC. It is shown that the hadron resonance gas model describes the energy dependence, as well as the lack of centrality dependence, qualitatively. The values of ET/Nch are related to the chemical freeze-out criterium E/N≈1 GeV valid for primordial hadrons. 相似文献
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Arijitt Borthakur Sridhar R. Charagundla Andrew Wheaton Ravinder Reddy 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(2):1378-316
T1rho-weighted MRI is a novel basis for generating tissue contrast. However, it suffers from sensitivity to B1 inhomogeneity. First, excitation with a spatially varying B1 causes flip-angle artifacts and second, spin locking with an inhomogeneous B1 results in non-uniform T1rho contrast. In this study, we overcome the former complication with a specially designed spin-locking pulse sequence and we successfully obtain T1rho-weighted images with a surface coil. In this pulse sequence, the spin-lock pulse was divided into segments of equal duration and alternating phase. This "self-compensating" T1rho-preparatory pulse sequence was analyzed and the effect of an inhomogeneous B1 field was simulated using the Bloch equations. T1rho-weighted MR images of a phantom and a human knee joint in vivo were obtained on a clinical scanner with a surface coil to demonstrate the utility of the pulse sequence. The self-compensating T1rho-prepared pulses sequence resulted in substantially reduced image artifacts compared to the conventional, single-phase spin-lock pulse. 相似文献
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McConnell TL Wheaton CA Hunter KC Wetmore SD 《The journal of physical chemistry. A》2005,109(28):6351-6362
Complexes between ammonia, water, or hydrogen fluoride and adenine, guanine, or their 8-oxo derivatives are investigated using density-functional theory. The binding strengths of the neutral and (N9) anionic complexes are considered for a variety of purine binding sites. The effects of hydrogen-bonding interactions on the (N9) acidity of the purine derivatives are considered as a function of the molecule bound and the binding site. It is found that hydrogen-bonding interactions with one molecule can increase the acidity of purine derivatives by up to 60 kJ mol(-1). The (calculated) simultaneous effects of up to four molecules on the acidity of the purine derivatives are also considered. Our data suggest that the effects of more than one molecule on the acidity of the purines are generally less than the sum of the individual (additive) effects, where the magnitude of the deviation from additivity increases with the number, as well as the acidity, of molecules bound. Nevertheless, the increase in the acidity due to additional hydrogen-bonding interactions is significant, where the effect of two, three, or four hydrogen-bonding interactions can be as large as approximately 95, 115, and 130 kJ mol(-1), respectively. The present study provides a greater fundamental understanding of hydrogen-bonding interactions involving the natural purines, as well as those generated through oxidative DNA damage, which may aid the understanding of important biological processes. 相似文献
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Jianyong Zhang Jagadese J. Vittal William Henderson Jessica R. Wheaton Iris H. Hall T. S. Andy Hor Yaw Kai Yan 《Journal of organometallic chemistry》2002,650(1-2):123-132
Modified Mannich reactions of amines, amino acids and a model peptide with Ph2PH and CH2O gave bis(diphenylphosphinomethyl)amines (Ph2PCH2)2NR [R=Ph (1), CH2CH2OH (2), CH2COOCH2Ph (3), CH2CONHCH2COOCH2Ph (4), CH2COOH (5)] and (Ph2PCH2)2NCH2CH2N(CH2PPh2)2 (6). Reaction with [ReBr3(CO)3]2− under mild conditions led to [ReBr(CO)3]{(Ph2PCH2)2NR} [R=Ph (7), CH2CH2OH (8), CH2COOCH2Ph (9), CH2CONHCH2COOCH2Ph (10), CH2COOH (11)] and [ReBr(CO)3(Ph2PCH2)2NCH2]2 (12). All new complexes have been characterized by NMR and IR spectroscopy and for 7, 9 and 10, single-crystal X-ray diffraction analyses. Electrospray mass spectrometric studies show that the rhenium–phosphine chelates are very stable, especially in neutral methanolic solution. Hydrolysis of the ester and amide linkages slowly occur in acidic and basic solutions over several weeks; displacement of the bromide ligand also occurs in basic medium. Cytotoxicity testing of 7–10 and 12 showed that all the complexes are active against specific tumor cell lines, especially MCF-7 breast cancer and HeLa-S3 suspended uterine carcinoma. 相似文献
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The hydrogen-bonding and stacking interactions of hypoxanthine, a potential universal nucleobase, were calculated using a variety of methodologies (CCSD(T), MP2, B3LYP, PWB6K, AMBER). All methods predict that the hydrogen-bonding interaction in the hypoxanthine-cytosine pair is approximately 25 kJ mol(-1) stronger than that in the other dimers. Although the calculations support suggestions from experiments that hypoxanthine preferentially binds with cytosine, the trend in the calculated hydrogen-bond strengths for the remaining natural nucleobases do not show a strong correlation with the experimentally predicted binding preferences. However, our calculations suggest that the stacking interactions of hypoxanthine are similar in magnitude to the hydrogen-bonding interactions at all levels of theory (with the exception of B3LYP, which incorrectly predicts stacked dimers to be unstable). Therefore, stacking interactions should also be considered when analyzing the stability of DNA helices containing hypoxanthine and the use of larger models that account for both hydrogen-bonding and stacking within DNA duplexes will likely result in better agreement with experimental observations. For the majority of the dimers, PWB6K and AMBER provide reasonable binding strengths at reduced computational costs, and therefore will be useful techniques for considering larger models. 相似文献
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The centrality dependence of thermal parameters describing hadron multiplicities and intermediate-mass dilepton spectra in heavy ion collisions at SPS and RHIC is analyzed. From experimental hadron multiplicities we deduce evidence for strangeness saturation at high energy and maximum centrality. The observed dilepton spectra can be parameterized by a centrality independent temperature. 相似文献
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M. F. Chancel F. A. Lewis J. E. Stacey Jones O. L. Barneby D. F. Calhane T. C. Wheaton G. Wegelin O. Brunck G. Oesterlein W. v. Bolton J. Compagno A. Fischer A. Sieverts W. Wippelmann E. F. Smith Cl. Winkler E. Jänecke O. Brill Cl. Br. Evans E. Bose F. Conrat F. Emich J. Donau R. Heinze R. Belasio 《Analytical and bioanalytical chemistry》1914,53(11):696-700
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